Phylum Arthropoda
chitin exoskeleton
jointed appendages
repeated segments
open circulatory system
more than 10 million species
respiratory system varies with subphlyum
Science Mag - Life's Pagent Not so Rich
Arthropods are everywhere
Two out of every three known species of animals
are arthropods
Members of the phylum Arthropoda are found in
nearly all habitats of the biosphere
news.sciencemag.org www.brighthub.com
Arthropod Origins
The arthropod body
plan consists of a
segmented body, hard
exoskeleton, and jointed
appendages, and dates
to the Cambrian
explosion (535–525
million years ago)
Early arthropods – the
Trilobites show little
variation from segment
to segment
Arthropods have an open circulatory system in
which fluid called hemolymph is circulated into
the spaces surrounding the tissues and organs
A variety of organs specialized for gas exchange
have evolved in arthropods
Molecular evidence suggests that living
arthropods consist of four major lineages that
diverged early in the phylum’s evolution:
– Subphylum Cheliceriforms (sea spiders,
horseshoe crabs, scorpions, ticks, mites, and
spiders)
– Subphlym Mandibulata
• Class Myriapods (centipedes and millipedes)
• Class Hexapods (insects and relatives)
• Class Crustaceans (crabs, lobsters, shrimps,
barnacles, and many others)
Arthropoda: Cheliceriforms
Cheliceriforms,, are named for clawlike feeding
appendages called chelicerae
Most marine cheliceriforms (including
eurypterids) are extinct, but some species
survive today, including horseshoe crabs
Fig. 33-30
www.enchantedlearning.com -
Cheliceriforms
Horseshoe
crabs (class
Merostomata)
Arthropoda: Cheliceriforms
Most modern
cheliceriforms are
arachnids, which
include spiders,
scorpions, ticks, and
mites
Scorpion
Dust mite
spider
50 µm
Class Arachnida – Closer look at the
Order Araneae
abdomen and a cephalothorax, which has six
pairs of appendages, the most anterior of
which are the chelicerae (4 pairs legs)
Gas exchange in spiders occurs in respiratory
organs called book lungs
www.education.com
Many spiders
spin silk
others are
ambush
predators or spin
a funnel and wait
for prey to fall
into the trap
http://upload.wikimedia.org/wikipedia/co
mmons/f/f9/Spiders_Diversity.jpg
Class Arachnida – Closer look at the
Order Solifugae
Contrary to popular myth, these
scary looking Arachnids do not
possess venom, nor do they eat
American solders or camels.
http://www.camelspiders.net/large-camel-spider-picture.htm
Urban Legends - Camel
Spider
Arthropoda: Myriapods
Myriapods are terrestrial,
and have jaw-like
mandibles
Millipedes, class
Diplopoda, Each trunk
segment has two pairs of
legs
Centipedes, class
Chilopoda, are
carnivores
They have one pair of
legs per trunk segment
Arthropoda: Class Hexapoda Insects
The Hexapoda, (insects) has more species than
all other forms of life combined
They live in almost every terrestrial habitat and in
fresh water
bioinf.nuim.ie
Fig. 33-35
Abdomen Thorax Head
Compound eye
Antennae
Heart
Dorsal artery Crop
Cerebral ganglion
Mouthparts
Nerve cords
Tracheal tubes Ovary
Malpighian tubules
Vagina
Anus
Flight is one key to the great success of insects
An animal that can fly can escape predators, find
food, and disperse to new habitats much faster
than organisms that can only crawl
In incomplete
metamorphosis, the
young, called nymphs,
resemble adults
Insects with complete
metamorphosis have
larval stages known by
such names as
maggot, grub, or
caterpillar
Insects undergo metamorphosis during their
development
Arthropoda: Crustaceans
Crustaceans typically have
branched appendages that are
extensively specialized for
feeding and locomotion
Most crustaceans have
separate males and females
While arachnids and insects thrive on land,
crustaceans, for the most part, have remained in
marine and freshwater environments
Isopods include terrestrial, freshwater, and
marine species
– Pill bugs are a well known group of terrestrial
isopods
– Some others are freakish parasites!
http://www.treehugger.com/natural-sciences/bizarre-tongue-
eating-parasite-discovered-off-the-jersey-coast.html